THE YOUNG 
no advantage in favor of hardness of surface by 
case-hardening at too high a temperature, as this 
impairs the quality of the bone by prematurely ex- 
hausting it, and driving off some of its combining 
elements, and great heat is also sure to warp the 
work. Gun-lock work, if properly done, comes out 
quite true for fitting in place. " 
An Instructive Experiment. — To prove that 
the inner dark portion of an illuminating flame 
contains combustible gases, the general practice 
with experimenters is to insert into that part of 
the flame a glass tube, so inclined that a portion of 
these gases shall rise into it, and thereupon 
igniting them at the further extremity of the tube, 
or leading the contents of the tube by an aspirator 
into a convenient vessel, when its combustibility 
can then be directly tested. Mr. Heuman has 
communicated to the Gei-man Chemical Society j 
another method, and a simpler one, of accomplish- 
ing the result, which seems worthy of notice. 
He recommends taking advantage of the well- 
known fact that a mixture of about four parts of 
chlorate of potassa and one part of strontium 
nitrate, heated to fusion, will burn with a very in- 
tense flame in hydrogen or illuminating gas, when 
once the ignition of the oxygen liberated from this 
mixture is effected by contact with a flame. 
To perform this very pretty experiment, the 
author states that it is only necessary to fuse a 
small quantity of the mixture in question in a little 
spoon at the apex of a luminous gas flame, and 
then to lower it into the dark portion, when a bril- 
liant combustion will immediately ensue; while, 
when removed to the luminous portion of the flame, 
or taken altogether out of it, it is at once extin- 
guished.— JbwrnaZ of the Franklin Institute. 
BOOK NOTICES. 
Manual of Telegraphy. Designed for begin 
ners. By Prof. J. E. Smith. Thirteenth Edition. 
New York: L. G. Tillotson & Co., 8 Dey Street, 
Telegraphy always has a peculiar charm for 
young people. Indeed we can think of nothing 
that will give more amusement than a short tele- 
graph line connecting two families. The cost and 
labor of putting up such a line is very slight, and 
the manual named above gives such full and simple 
directions that any boy can follow them. 
The Outlines of Natural Philosophy. For 
Young Children. By Edwin J. Houston, A. M. 
Philadelphia: Claxton, Remsen & Haffelfinger. 
One of the most difiicult tasks that one can un- 
dertake is to give such clear and simple explana- 
tions of the principles of Natural Philosophy as will 
be easily understood by children. Most of those 
who have attempted this task have failed from one 
of two causes: Either the explanations were er- 
SCIENTIST. 99 
roneous, or they were beyond the comprehension 
of those to whom they were addressed. It seem» 
to us, after a careful examination, that the author 
of the work before us has succeeded in avoiding 
both these errors, and he has consequently pro- 
duced a book which must prove a great boon to 
parents who have intelligent children, eager for a 
knowledge of the material world around them. To 
such we would cordially recommend the little book 
on our desk. For the purpose intended it is cer- 
tainly the best that we know of. 
Ot£ on a Comet! A Journey through Planetary 
Space. (A sequel to "To the Sun.") From the 
French of Jules Verne, By Edward Roth. With 
thirty-six full page illustrations. Philadelphia: 
Claxton, Remsen & Haffelfinger, 
We hope none of our readers will treat this book 
j as a certain staid old gentleman treated another of 
Jules Verne's works. After reading a few pages, he 
threw it down in disgust, and declared that he 
could not believe one word of it 1 However much 
the story may do violence to our sense of proba- 
bility, or even of possibility, it is nevertheless un- 
deniable that a great deal of the book is absolutely 
true. Like all works of art, it brings before us 
conditions of an unusual character, but of a higher 
grade than any that are likely to occur under ordi- 
nary circumstances. In the present instance we 
are brought face to face with the great laws of 
nature, operating under conditions such as no 
human experience ever real'zed. Our readers will 
find in this book not only an interesting story of 
strange adventures, but a great many new ideas in 
regard to the mechanism of the heavens. Through 
the whole there runs a vein of humor and anecdote 
which greatly relieves the dryness of the scientific 
discussions. 
Inquiries. 
29. Can you give me a recipe for nickel or silver 
plating metals, with or without a batter}? Will an 
electro-galvanic battery (shocking machine) serve 
the purpose of battery in plating wares? I manu- 
factured one of your ten-cent batteries; it works 
like a charm, and I would like to know some ex- 
periments to try with it. J. N. H. 
Answers. 
30. In as concise a manner as possible, I shall 
attempt to answer an inquiry which appears in 
letter 27. The cheapest apparatus for charging a 
Leyden jar is the following: Place an ordinary iron 
tea tray on a perfectly dry tumbler; then warm a 
sheet of paper as hot as possible by passing it sev- 
eral times over a gas light, or by holding to a stove. 
Lay the paper on a board or otbnr non-conducting 
surface, and rub it vigorously with a piece of india- 
rubber. Spread the paper on the waiter, to which 
the jar should now be apphed. If the weather ie 
